Multiple sensing device and sensing devices therefor

ABSTRACT

A multiple sensing device has sensors, mounted on a common rotatable shaft, for sensing magnetic field, electric field, gas flow, angular acceleration and linear acceleration. The latter three of the sensing devices employ piezo electric crystals as the sensors, while the magnetic field sensor employs a pair of rotating coils and the electric sensing device employs a pair of rotating electrodes.

BACKGROUND OF THE INVENTION

This invention relates to sensing devices for physical characteristics,and is more particularly directed to a low cost sensing device forsensing such parameters as magnetic field, electric field, gas flow,linear acceleration and angular acceleration. The invention isparticularly directed to simplified devices or combination of devices ofthis type, which are particularly adaptable for use in aircraft. Itwill, of course, be apparent that the invention may be advantageouslyemployed in other fields.

While devices are known for the detection of each of these parameters,in general the devices are relatively expensive, so that their use isrestricted, and they are not adaptable to application having limitedlife. The present invention is therefore directed to the provision of anovel multiple sensing device of low cost, which is capable ofaccurately sensing all of these above parameters. The invention is alsoconcerned with the provision of separate sensing devices for sensingeach of these parameters.

SUMMARY OF THE INVENTION

Briefly stated, in accordance with the invention, one or more sensingdevices is mounted for rotation on a shaft, and commutator means areconnected to enable coupling of the sensed voltage from the sensingdevice. The sensing devices are adapted to produce alternating voltagesignals, the instantaneous maximum amplitudes of the signalscorresponding generally to the vector of the measured physicalcharacteristic in a given plane, such as a plane normal to the axis ofrotation. As a consequence, substantially complete data regarding thephysical characteristics may be provided by employing two of themultiple sensing devices.

In accordance with the invention, a magnetic field sensing device, fordetermining a magnetic field vector normal to the shaft, comprises apair of magnetic coils symmetrically affixed to rotate with the shaft. Asensing device for ascertaining the vector of an external electric fieldmay comprise a pair of electrodes mounted for rotation with the shaft,with the external ends of the electrodes being uninsulated. Gas flow,such as air flow, in a direction normal to the axis of the shaft may bedetected by a crystal plate mounted, preferably on the end of the shaft,this crystal being bendable about an axis parallel to the plate andnormal to the shaft. Angular acceleration about axes normal to the shaftmay be detected by a pair of crystals extending radially from the shaft,and having bending axes normal to the shaft. The radially outerextremities of the latter crystals may be joined by a symmetrical, i.e.annular, reaction mass. In addition, linear acceleration normal to theshaft may be obtained by a pair of similar crystals compressable in adirection normal to the axis of the shaft. Masses may also be providedat the radial outer extremities of these crystals.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention will be more clearly understood, it will nowbe disclosed in greater detail with reference to the accompanyingdrawings, in which:

FIGS. 1-5 are simplified illustrations of magnetic field, electricfield, gas flow, linear acceleration and angular rate sensing devicesemployed in accordance with the invention;

FIGS. 6A-6D are views illustrating, in simplified form, four consecutivepositions of the sensing rotor of FIG. 5;

FIGS. 7A-7D are figures illustrating, consecutively, the side viewscorresponding to the views of FIGS. 6A-6D, respectively;

FIG. 8 illustrates the output of the two crystals of FIGS. 6A-6D and7A-7D;

FIG. 9 illustrates the sum of the voltages generated as illustrated inFIG. 8;

FIG. 10 is an exploded cross-sectional view of a portion of amulti-probe assembly in accordance with a preferred embodiment of theinvention;

FIG. 11 is a cross-sectional view of an electric motor rotor that may beemployed in combination with the system of FIG. 10;

FIG. 12 is a cross-sectional view of a multi-probe assembly,incorporating the elements of FIG. 10;

FIG. 13 is a cross-sectional view of a further embodiment of amulti-probe assembly, in accordance with the invention; and

FIG. 14 is a simplified illustration of one application of a pair ofmulti-probe assemblies in accordance with the invention, on an aircraft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to the provision of a multiple sensingdevice, particularly adaptable for use on aircraft, but which many ofcourse have other applications. The concept of a multiple sensing devicefor physical parameters necessitates the combination of individualsensing devices adaptable to combination, for sensing purposes, in anaccessable manner, in order to achieve the desired end result, and hencethe present invention of necessity incorporates a member of individualsensing elements responsive to different physical characteristics. Theindividual sensing devices may, of course, have separate utility, eventhough they are particularly adaptable to being combined for the desiredpurpose.

Referring now to the drawings, FIGS. 1-5 illustrate in simplified formthe principles of operation of the five sensing devices with which thepresent invention is primarily concerned. It will, of course, beapparent that a multiple sensing device in accordance with the inventionmay additionally incorporate other sensing means, or that, when desired,one or more of the illustrated sensing means may be omitted.

As those treated in FIG. 1, a magnetic field sensing device is comprisedof a pair of identical coils 10 mounted in a column plane on oppositesides of a shaft 11, for rotation with the shaft. Assuming the shaftextends into the coordinate direction Z and that the coils are connectedexternally by way of a suitable commutator, the device of FIG. 1 willproduce an alternating voltage of a frequency corresponding to therotary speed of this shaft, and having an instantanteous peak when theplane of the coils is aligned with an external magnetic field, such asthe earth's magnetic feld. The magnitude of the output voltage isdependent upon the component of the external magnetic field in the X/Yplane. In the arrangement of FIG. 1, it is apparent that the greatestportion of the output voltage is developed by the radially outermostportions of the coils.

The output voltage is a sign wave when the field is linear. When theincident magnetic field is not linear, i.e. contains gradients,harmonics of the fundamental are generated. In the simple case, thesecond harmonic is the most dominant. In effect, the main field and thegradient fields give uniquely different signal frequencies.

In the electric field sensor illustrated in FIG. 2, a pair of electrodes12 extend radially in opposite directions from the shaft 11, with theradiantly outermost portions of the electrodes being uninsulated. Theradiantly intermediate portions of the electrodes are preferablyinsulated. It is apparent that, with the inner ends of the electrodesconnected externally of the device by way of a suitable commutator, thedevice will produce a sine wave voltage output of a frequencycorresponding to the rate of rotation of the shaft 11. The voltagearises from the fact that the non-insulated radially outer ends of theelectrodes 12 rotate in a static electric field, such as the staticelectric field of the earth, whereby the instantaneous maximum of thesine wave voltage output occurs when the electrodes are aligned withthis electric field. The amplitude of the voltage corresponds to thegradient of the static electric field in the X/Y plane.

In the sensing device of FIG. 3, a plate piezo electric crystal 13 ismounted on one end of the shaft 11 for rotation therewith. The plane ofthe crystal 13 is parallel to the axis of the shaft 11, and the crystalis arranged so that it may be bent about axes normal to the axis of theshaft 11. Suitable electrodes of conventional nature (not shown) areaffixed to the crystal, so that stress upon the crystal normal to theshaft 11 results in the generation of a piezo electric voltage, whichmay be directed externally of the device by a suitable commutatorassembly. If a component of a gas flow is in the X/Y plane of thedevice, it is apparent that the gas flow, impinging upon the crystal,will stress the crystal so that an alternating voltage will be produced.The alternating voltage will have a frequency corresponding to the rateof rotation of the shaft 11 with the instantaneous peaks occurring whenthe bending axis of the crystal is normal to the component of the gasdirection in the X/Y plane. The crystal may be referred to as a "bender"crystal. The amplitude of the voltage corresponds to the component ofthe gas flow in the X/Y plane, assuming, as above, that the shaftextends in the Z direction. In the arrangement of FIG. 3, the crystalthus serves as a restoring spring and a signal generator, and may beadvantageously employed as an air mass data probe.

In FIG. 4, a pair of crystals 14 are mounted on opposite sides of theshaft 11, for rotation therewith. The crystals 14 are oriented to becompressible in a direction normal to the shaft 11. If desired, suitablemasses 15 may be provided at the radially outer extremities of thecrystals 14. If suitable leads are connected conventionally to thecrystals 14, and directed externally of the device by way of a suitablecommutator assembly, it is apparent that an alternating output voltagewill be produced having a frequency corresponding to the rate ofrotation of the shaft. The instantaneous maximum of the voltage occurswhen the crystals are aligned with a component of linear acceleration inthe X/Y plane, and the amplitude of the output voltage thus correspondsto the linear acceleration of the shaft in the X/Y direction. Thesensitive axes of the crystals are thus oriented to react toacceleration parallel to the spin plane of the device. The two crystalsare electrically interconnected in order to provide an additive outputfor these two elements.

In FIG. 5, two crystals 16 are also mounted on opposite sides of theshaft 11. In the arrangement of FIG. 5, however, the crystals aremounted to be bendable, and having bending axes normal to the axis ofthe shaft. If desired, a reaction mass such as annular mass 17 may beprovided symmetrically at the radially outer ends of the crystals. Thearrangement of FIG. 5 constitutes an angular velocity probe, based uponthe gyroscopic operation of an elastically restrained body rotating athigh velocity. The initial member and the restoring springs thusconstitute the same element, as in the case of the air mass data probeof FIG. 3 and the linear acceleration probe of FIG. 4. The two bendercrystals are arranged in a dipole fashion for common mode rejection andinertial balance. In the arrangement of FIG. 5, angular momentum of themasses reacting as a result of an applied angular velocities at rightangles to the spin axis of shaft 11, results in the generation of avoltage by the crystals which is sinusoidal in distribution and exhibitsa frequency identical to the rate of rotation of the shaft. The twocrystals of the arrangement of FIG. 5, are preferably interconnected totheir respective commutators in the opposite sense from that of thedevice of FIG. 4.

The operation of the rate gyro of FIG. 5 may be more readily understoodwith reference to FIGS. 6-9. Thus, FIGS. 6A-6D represent fourconsecutive positions of the crystals, with counterclockwise revolution,as may be seen from the end of the shaft 11. In these figures, the twocrystals are identified as crystals 16' and 16". The shaft is assumed tobe continuously rotating. Referring to FIG. 7, which depicts a side viewof the device of FIG. 6, it is assumed that the axis of the shaft 11 hasbeen displaced through an angle alpha. The shaft 11 and the hub 18 onthe shaft in which the crystals 16' and 16" are mounted, are adequatelyrigid so that they both may substantially instantaneously exhibit theirnew positions without deformation. The radially outer ends of thecrystals, however, due to gyroscopic action, remain for some timeoriented as though the angular displacement of the shaft 11 had notoccurred. This is, of course, particularly true if a reaction mass islinked to the radially outer ends of the crystals. As a consequence ofthe gyroscopic action, the crystals bend about their mechanical axes, asillustrated in FIGS. 7A-7D, respectively, to result in output voltagesas illustrated in FIG. 8. It is thus seen that the instantaneous peaksof the resultant alternating voltage occur when the crystals extendnormal to the axis of rotation about the angle alpha. Since the outputsof the crystals are of different polarity, the crystals areinterconnected in reverse senses, to produce the resultant outputvoltage as illustrated in FIG. 9.

In the arrangement of FIGS. 5-9, it is apparent that the crystals areemployed as gyroscopic elements, with or without the provision of areaction mass, and that the strain on the crystals is proportional toinput angular rate. The amplitude of the output is proportional to theinput angular rate, and the phase of the output is related to thedirection of the input angular rate of angular displacement of therotating shaft in a direction normal to the axis of the shaft. In otherwords, if the shaft 11 is angularly displaced about an axis in the X/Yplane, the output of the rate gyro or angular velocity sensor of FIG. 5is proportional to the rate of rotation about the axis in the X/Y plane,then the phase of the output voltage is related to the orientation ofthe axis of rotation in the X/Y plane, assuming again that the shaft 11extends in the Z direction.

FIG. 10 is an exploded partially cross sectional view of a portion of amulti-probe assembly in accordance with a preferred embodiment of theinvention. This view illustrates primarily the rotor components, to showthat they can be of modular construction, whereby a multi-probe assemblymay be fabricated of any of the desired sensing probes. It will ofcourse be apparent that the cover construction for such a multi-probeassembly will be dependent upon the components chosen for use in theassembly.

As illustrated in FIG. 10, the multi-probe assembly is comprised of anair data probe 30, an electric field probe 31, a magnetic field probe32, an angular velocity and linear acceleration probe 33, and a slipring 34 and brush block assembly 40. In addition, the assembly includesa gas drive ring 35 for the pneumatic drive of the rotor. All of theelements of FIG. 10, except the brush block assembly 40, constitutes apart of the rotor.

The gas drive assembly 35 may be comprised of a metallic ring 41 havinggas drive slots 42 on its radially outer periphery, whereby the ring maybe rotated by directing a jet of air tangentially against this outerperiphery. The ring 41 has a recess 43 in one face thereof, forreceiving the magnetic field probe 32. In addition, a circular coaxialrecess 44 is provided in the other face for receiving the angularvelocity and linear acceleration probe 33.

The magnetic field probe is comprised of a circular disc 50 ofinsulating material, within which the two magnetic sensing coils 51 and52 are embedded. The coils 51 and 52 have radially outer extremities 53which extend axially of the disc for substantially its full axialdimension. The coils 51 and 52, which are identical, have radial returnssquashed down axially, as illustrated in FIG. 10, with the axialextension of the radial innermost portions of the coil being at aminimum. As a consequence, the radial returns are so positioned withrespect to the spin axis of the device that the axial return is near thecenter of rotation. This in effect gives the section line at the majorradius most of the charge generating capacity for the probe. The disc 50is fitted, by suitable conventional means, for rotation on a shaft 54.The shaft 54 is preferrably hollow, and serves as a bearing for theassembly, to extend through a housing (not shown in FIG. 10). Suitableinterconnecting wires for the coils 51 and 52, as well as forinterconnecting the coils to the slip ring assembly, are illustrated at55.

The shaft 54 may be affixed only to the magnetic sensing assembly, withthe ring 50 being fitted tightly for rotation in the recess 43.Alternatively, the shaft 54 may extend through the ring 50 and be fittedto the gas drive ring 41.

The electric field probe 31 and the air data probe 30 are adapted tosense data which requires their physical location outside of the housingof the device. Consequently, the electric field probe may be comprisedof an insulating disc 58 having a central bore adapted to fit over theshaft 54. The disc 58 may be connected to the shaft 54 for rotation byany conventional means. The disc 58 has a pair of radially extendingholes 59 through which the electrodes 60 extend. Suitable enlarged ends,such as conductive balls 61, may be provided at the ends of theelectrodes 60 for sensing the earth's static electric field. The innerends of the electrodes 60 extend into a recess 62 in the face of thedisc 58, for interconnection with conductors 63 extending through theshaft 54, the conductors 63 advantageously extending completely throughthe device for interconnection with the slip rings 64 of the slip ringassembly 65.

As will be apparent from the following disclosure, a portion of thehousing of the device may extend between the magnetic field probe andthe electric field probe.

The air data probe is also comprised of an electrically insulatingrotating body member 70 having a disc shaped base adapted to fit forrotation either into the recess 62 of the electric field probe or, ifdesired, directly on the end of the shaft 54. The body 70 may be anaxial extension 71 for enclosing a crystal 72. A further crystal 73extends beyond the insulating body 70, to serve as the air flow sensoras above described. The crystal 72 within the extension 71 serves as areference, and is thereby interconnected differentially with the crystal73. The conductor connected to these crystals may be led to a connector74 affixed in the base 70, for interconnection with the slip ringconductors 63.

The angular velocity and linear acceleration probe may form a combinedunit 33, as illustrated in FIG. 10. For this purpose, the assembly maybe comprised of a cylindrical housing 76 adapted to be fitted forrotation in the recess 44 of the gas drive ring. The housing 76 maycontain a pair of radially extending crystals 77 at a central portion,extending to a hub 78, to serve as the linear acceleration probe asdiscussed in accordance with the above principles. The linearacceleration probe is disposed axially centrally of the device 33. Inaddition, a plurality of pairs of bender crystals 79 may be positionedaxially on each side of the linear acceleration probe, for the sensingof angular velocity as discussed above. Suitable conventional conductorsare provided (but this is not shown) connected to the crystals, forinterconnection with the slip ring assembly 65.

The slip ring assembly 65 may be fitted directly to the lower end of theassembly 33, for example, on studs 80 on the lower end of the assembly33, in order to complete the rotary structure of the device. The slipring assembly has a plurality of slip rings 64, adapted to be connectedto each of the sensing probes as above discussed. While the drawing ofFIG. 10 does not show these conductors, it is apparent that suitableapertures may be provided in the housings of the structure, for enablingthe necessary interconnections. For this purpose, it is of course notnecessary that a single shaft extend throughout the rotor assembly,since the individual components of the structure may be provided withinternally embedded conductors for this purpose. As a consequence, it isapparent that a modular construction may be achieved, whereby theelements may be interconnected as desired.

While the brush block 40 for cooperation with the slip ring assembly 34is not a rotary member, it has been illustrated in simplified form inFIG. 10, to illustrate in general a preferred manner by which thesignals generated in the various probes may be led externally of thedevice. The slip rings 64 may be at the axial end of the slip ringassembly, axially beyond a bearing portion 81 of the rotor assembly, inorder to simplify construction of the device.

In the use of the device in accordance with the invention, it is ofcourse necessary to establish the phases of the different alternatingvoltages generated by the sensing devices, in order to be able toascertain the directions of the various sensed physical quantities. Forthis purpose, in accordance with one embodiment of the invention,reference markings 82 may be provided on one face of the gas drive ring41, for cooperation with a suitable sensing device, such as aphotoelectric sensing device 123 of conventional nature as illustratedin FIG. 13. It will of course be apparent that any other forms ofreference generated of conventional nature may alternatively be employedin combination with the multi-probe device of FIG. 10.

While the device of FIG. 10 is particularly adaptable for gas drive, itwill be apparent that it may also be employed with an electric motordrive. For this purpose, the gas drive ring 41 is provided with anannular recess 85 radially outwardly of the recess 44. A motor rotor 86for example as illustrated in FIG. 11, may be mounted in the recess 85,for rotation with the rotor. The recess 85 has a sufficient radialdimension that a stator assembly affixed to the housing (not shown inFIG. 10) may also be fitted into recess 85. For example, the stator mayextend axially from the end housing of the assembly. It is thereforeapparent that the device of FIG. 10 may be modified for electric drivewith a minimum of modification.

FIG. 12 shows the assembly of FIG. 10 in cross section, with theelements of the rotor interconnected together in their preferred form.In addition, it shows the brush block assembly 40 mounted in a recess ininsulating housing, 90, for cooperation with a slip ring assembly. Thehousing member 90 serves as one cover of the device, and is bolted to ametal base block 91, for example, to enable the rigid mounting of thedevice as desired. In addition, the central portion of the housing 92 isaffixed to the base 91. The housing 90 is provided with suitablebearings 93, to engage the portion 81 of the shaft of the rotor. Theupper portion 94 of the housing, which serves as a cover, extendsbetween the magnetic and electric field sensor, and is provided withbearings 95 for the shaft portion 54. The portion 92 and 94 of thehousing may also be of insulating material.

The arrangement of FIG. 12 is adapted for gas drive, and for thispurpose the housing 92 is provided with a gas drive inlet 96, positionedto direct air or other gas against the turbine blades of the gas drivering 41. An outlet for the gas may extend by way of an aperture 97 inthe lower cover 90, which communicates with an aperture 98 in themounting base 91.

As discussed above, the multi-probe sensor in accordance with theinvention may be formed of a lesser number of components. Thus, asillustrated in FIG. 13, the multi-probe sensor is comprised of a rotaryunit incorporating only a pair of bender crystals 100 mounted forrotation with a shaft 101. The crystals 100, as is apparent in FIG. 13,do not extend inwardly to the shaft, their bases being fixed in asuitable block or hub 102 radially outwardly spaced from the shaft 101proper. In the arrangement of FIG. 13, the hub or blocks 102 are affixedto one side of a web of the gas drive ring 103, and a further hub orset-up blocks 104 is provided on the other side of the web. From theseblocks or hub a pair of additional bender crystals 105 are providedextending radially inwardly. The inner ends of these latter crystals arenot rigidly affixed to any component of the structure. The crystals 105are mounted so that they are bendable about axes parallel to the shaft101. As a consequence the output of the crystals 100 corresponds toangular rate and the output of crystals 105 corresponds to acceleration.

A gas inlet 110 is provided in the housing 111 for driving the shaft101. In addition, the reference generator 120, discussed above, ismounted in the housing 111 for cooperation with the suitable referencescale 121 on a face of the gas drive ring 103. The reference generatormay comprise a reference source of light 122, such as an LED,cooperating with a suitable photosensitive device 123 of conventionalnature, for producing a reference signal output related to the positionof the rotor of the device. The device of FIG. 13 is provided with asuitable slip ring and brush assembly 125.

It will of course be apparent that other combinations of units may beemployed, in accordance with the invention.

Since the multi-probe sensor in accordance with the invention providestwo axis data, a pair of such multi-probe assembly may be employed toprovide all the necessary three-dimensional data with respect to themeasured physical quantity. This is particularly useful, for example, inaircraft. Thus, as illustrated in FIG. 14, a pair of multi-probe devices130 of the type illustrated in FIGS. 10 and 12 may be mounted withorthogonal axes on an aircraft 131. This arrangement enables theinputting of sufficient data to the aircraft to enable the calculationof the earth's magnetic and electric field, as well as external air flowand linear acceleration and angular velocity of the aircraft. The probeassembly is inexpensive, and readily fabricated.

It is of course apparent that the electric circuits for comparison ofthe phase of the reference generator with the measured quantity may beof conventional nature, and hence need not be discussed in detail inthis specification.

Typical performance characteristics of a multi-probe assembly, inaccordance with the invention, are provided in Table 1 of thisdisclosure.

It is further apparent that this multi-probe assembly, in accordancewith the invention, by employing a single rotary shaft, reduces cost andpower consumption in the provision of needs for sensing the necessarydata, as well as a decrease in volume and mechanical complexity by anorder of magnitude. Further, it is apparent that the majority ofcomponents of the structure may be formed of molded plastic.

While the invention has been disclosed and described with reference to alimited number of embodiments, ti will be apparent that variations andmodifications may be made therein, and it is intended in the followingclaims to cover each such variation and modification as falls within thetrue spirit and scope of the invention.

    TABLE 1       I II III IV V VI VII  X/Y "Z" X/Y AIR ≮ AIR X/Y X/Y     PARAMETERS AXIS MAG AXIS MAG AXIS ELEC SPEED FLOW ANG.VEL. LIN. ACCEL.       SCALE FACTOR (V.D.C.) 5.V/GS 5.V/GS .017V/V/MTR .010V/MPH .165V/DEG     .017V/DEG/SEC .250V/"g" BIAS (TOTAL VECTOR) <.002 GS <.01 GS <3.V/MTR     <2.MPH <.5° <.02°/SEC <.002 "g" NULL UNCERT. (HR TO HR)     <.0005GS RMS <.0005GS RMS <.5V/MTR RMS <.3MPH RMS <.1°RMS     <.003°/SEC RMS <.0005"g" RMS NULL UNCERT. TRN ON TO  <.0008GS PP     <.0005GS PP <1.V/MTR PP <.5MPH PP <.25°PP <.008°/SEC PP     <.0008"g" PP TRN ON NULL UNCERT. SPIN VEL.  <.001GS PP <.0005GS PP     <1.V/MTR PP <2.MPH PP <.30°PP <.01°/SEC PP <.002"g" PP     VAR.±10% LINEAR OPERATING RANGE 1.0 GS 1.0 GS 300.V/MTR 500.MPH ±     30.° 300°/SEC 20 "g" MAX. OVERRANGE INPUT 5.0 GS 5.0 GS     1000.V/MTR 1000.MPH ±180° 1200°/SEC 100 "g" LINEARITY     %DEVIA. FR  <1.% <1.% <2.% <2.% <1.5% <1.% <.5% NOM. S.F. SYMMETRY     (SLOPE AGREEMENT) <1.% <1.% <2.%  -- <1.5% <1.% <.5% CROSS AXIS COUPLING     <2.%      -- <2.% BY THE COS. BY THE AMP- <2.% <.5%     OF AIRFLOW≮     LITUDE OF AIRSPEED CROSS QUANTITY ALIGNMENT <± .5°<±.5.degre     e. <±.5° <±.5° <±.5° <±.25°     0°(REF.) CROSS QUANTITY COUPLING I. X/Y AXIS MAG FIELD 100%  --     NEGL. NEGL. NEGL. NEGL. NEGL. II. "Z" AXIS MAG FIELD  -- 100%  "  "  "     "  " III. X/Y AXIS ELEC FIELD NEGL. NEGL. 100%  "  "  "  " IV. X/Y AIR     SPEED  "  " <.001V/MTR/MPH 100%  --  "  " V. ANGLE OF AIR FLOW  "  "     NEGL.  -- 100%  "  " VI. X/Y AXIS ANG VEL  "  "  " NEGL. NEGL. 100%     <.00005"g"/        DEG/SEC VII. X/Y AXIS LIN ACCEL  "  "  " <.02MPH/"g"     <.05°/"g" <.0002°/SEC/"g" 100%

What is claimed is:
 1. A gas flow sensing device comprising a rotatable shaft, a crystal mounted to extend axially from one end of said shaft, said crystal comprising a flat plate of a piezo electric material oriented in a longitudinal plane of said shaft, means for rotating said shaft, and commutator means coupled to said crystal, whereby said device produces an alternating output voltage having instantaneous peaks when the plane of said crystal is normal to the vector of flow of an external gas normal to said shaft.
 2. The device of claim 1 further comprising means for determining the angular displacement of said shaft.
 3. An air mass sensing device comprising a rotatable shaft, a sensing piezoelectric crystal cantilevered to extend coaxially with said shaft from one end thereof, said crystal extending axially in a longitudinal plane of said shaft, and means for rotating said shaft.
 4. An air mass sensing device comprising a body mounted to be rotatable about a given axis, a piezoelectric crystal mounted to said body to extend coaxially longitudinally from said body along the axis thereof, said crystal being cantilevered from said body, commutator means coupled to said crystal for receiving voltages therefrom, and means for rotating said body about said axis.
 5. The air mass sensing device of claim 4, further comprising a reference piezoelectric crystal within said body and extending along said axis, for providing a reference for said first mentioned crystal.
 6. The air mass sensing device of claim 5, wherein said body is an insulating body.
 7. A multiple sensing device comprising a housing, a rotatable shaft within said housing and extending through a wall thereof, a first piezoelectric crystal cantilevered on the end of said shaft outwardly of said housing, to extend coaxially with said shaft, for providing air mass data, and first and second groups of sensing piezoelectric crystals mounted within said housing for rotation with said shaft, for sensing linear and angular acceleration of said device.
 8. The sensing device of claim 7, further comprising an electric field sensing device mounted to rotate with said shaft between said housing and said end of said shaft.
 9. The multiple sensing device of claim 7, further comprising a magnetic field sensing device mounted to rotate with said shaft within said housing.
 10. The sensing device of claim 9, comprising a drive wheel mounted on said shaft, and pneumatic drive means positioned in said housing for directing a driving fluid against said drive wheel.
 11. The sensing device of claim 10, wherein said drive wheel has a first recess coaxial with said shaft for receiving said linear and angular acceleration sensing means, said device further comprising a magnetic field sensing device mounted in a further recess of said drive wheel. 